Process of reducing organic compounds



.. UNITED STATES NEW YORK, AS$IGNOB TO NATIONAL ANILINE.&

- 25 ficient to effect the '35 of the reduction Patented my 16,- 1929.

DONALD G. scenes, or HAMBURG,

CHEMICAL CO., INC., OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

PROCESS OF REDUCING ORGANIC COMPOUNDS.

. no Drawing.

' This invention relates to a method of reducin organic compounds by the action of a 'SllltitblQ metal and an inorganic salt ofisulfurous acid, more particularly sodium bisulfite, and is especially applicable to the reduction of indigo and other dyes, especially vat dyes, to the leuco state.

In the reduction of organic com by means of zinc and sodium bisu fite as heretofore proposed, wherein the organic compound is subjected to the action of zinc in conjunction with sodium bisulfite, the reaction which takes place, though not definitely established, may for theoretical purposes be conveniently represented by the following equation: I

It is well-known that the normal sulfites 2 of sodium'and zinc are produced during the course of the reaction, and in amounts substantially in accord with this equation.

Heretofore proposed processes which use zinc and an initial amount of sodium bisulfite sufdesired reduction are not economical since most, if not all, of the bisulfite is lost in its transformation to normal sulfite.

Accordin to the present invention, the

normal sul tes present or produced in the above reaction, are converted into bisulfites and thereby permitted to enter into reaction with a further quantity of zinc. This is accomplished by introducing during the course an acid, such as sulfuric or hydrochloric acid, in amounts sufficient to completely or partly convert the sulfites to bisulfites.

Theintroduction of an excess of sulfuric I 4 or hydrochloric acld over that requiredfto just transform the sulfites into bisulfites is preferably avoided since it may lead to side reactions and the production of undesirable by-products. Without limiting the inven- 5 tion to any particular theory, the following e nation is given as representing the reaction w ich may be regarded as taking place in the conversion of the normal sulfites to bisulfites.

ZnSO,+Na,SO,+H,SO,= ZnSO,,+2NaHSO .(2) As a result of adding an acid during the process, the amount of sodium bisulfite present during the reduction may be kept substanounds application filed March 5, 1920. Serial No. 92,614.

constant and equal to the amount initially introduced. This permits the initial emp oyment of but a fraction of the amount of sodium bisulfite necessary when no acid is used, an economic advantage which the present invention contemplates. Equations 1 and 2-may be combined, if desired, to indicate the course of the completed reaction:

Thus the reaction is substantially that of sulfuric acid'and zinc as regards materials consumed since the amount of sodium bisulfite present remains practically or approximately constant throughout. The chemical effect obtained, however, is that of bisulfite and zinc and not of acid and zinc since in the latter case the effect is usually, if not always, different.

In carrying out the present invention, theorganic compound to be reduced is brought tially into contact with the necessary quantity of zinc or other suitable metal (e. g., iron, magnesium, etc.) and an amount of sodium bisulfite which in itself is preferably insufficient in the absence of acid to complete the reaction, and to the well-stirred mixture at a suitable temperature there is added, either intermittently or continuously, an amount of sulfuric or hydrochloric acid, or other suitable acid, sufiicient to formor to maintain the presence of a bisulfite, an excess over this amount being preferably avoided. As a rule, a slight odor of sulfur dioxide is a sufficient test to serve as a control of the amount of acid added. When the reduction is complete, the product is isolated in any suitable manner.

The invention will be further illustrated by the following specific example, but it is understood that the invention is not limited thereto. The parts are by weight.

EmampZa-To a well-stirred solution of 17.3 parts of sodium bisulfite (100 percent purity or its equivalent calculated as pyrosulfite, Na S O in 320 parts of water there is added 319 parts of a 20 percent indigo paste and 16.7 parts of zinc dust (100 percent purity or equivalent) in the form of an aqueous slurry. Stir for about ten to fifteen minutes, heat the mixture to a temperature of about 6065 C., and maintaining this tempera ture, and with good stirring, slowly add about 85 parts of percent sulfuric acid at such a rate that a decided odor of sulfur dioxide is more or less continiiously percptible.

After all of the acid has been added, stir the mixture, while permitting it to cool to about 20-25 (l, for 6 to 8 hours or until substantially all of the zinc has dissolved. Filter off the leuco-indigo and wash with water.

Instead of adding the sulfuric acid continuously it may be added in small portions at a time. Additional amounts of zinc dust or of bisulfite may be added during the process if found desirable or necessary to complete the reduction. By this procedure, the neutral or normal sodium sulfite and zinc sulfite formed during the reduction by the action of the zinc on the bisulfite are converted by the sulfuric acid into sulfates and acid sulfites, that is, bisulfites, and the latter in turn react with further quantities of zinc. In this way, the amount of sodium bisulfite initially added to the reaction mixture need be only a relatively small amount, e. g., ten to fifty percent, more or less, of that required when'no sulfuric acid is employed. The temperature at which the reduction is carried out may vary but as a general rule high temperatures are to be avoided since loss of sulfur dioxide may occur due, in part, to the decomposition of the acid sulfite into normal sulfite. Further, the addition at any given moment of an amount of sulfuric acid in excess of that required to just convert all of the normal sulfites to bisulfites is preferably avoided since the best results appear to be obtained under these conditions ut more or less than this amount can be employed without departing from the spirit or scope of the invention.

For the purposes of this invention, it will be understood that any inorganic salt which yields a bisulfite upon treatment with an acid, or upon-oxidation, is regarded as equivalent to a bisulfite, and comes within the scope of this invention.

.In an analogous'manner, other dyes and other organic compounds may be reduced, for example, flavanthrone to its leuco compound, methyl violet to its leuco compound, nitrosalicylic acid to aminosalicylic acid, nit-robenzaldehyde to aminobenzaldehyde, etc.

copending application, Serial No. I

In my 711,047, filed May 5, 1924, for production of anthraquinone dyestuffs, I have described and claimed a specific application of the present invention to the reduction of a diaminodihydroxyanthraquinone disulfonic. acid for the production of the leuco compound of the corresponding diaminodihydroxyanthraquinone monosulfonic acid.

I claim:

1. A process of reducing an organic com- I pound which comprises mixing the organic compound with'zinc and a solution of sodinormal sulfite sulfite in. conjunction with zinc,

um bisulfite, the amount of sodium bisulfite being insufiicient to interact with all of the zinc present, and during the reaction continuously adding an amount of sulfuric acid to the mixture sufficient to form and maintain the presence of bisulfite from the normal sulfite present.

2. A process of reducing indigo which comprises mixing the indigo with zinc and a solution of sodium bis-tlfite and during the reduction adding sulfuric acid to the mixture to form bisulfite from the normal sulfite present.

3. In a process of reducing indigo, the steps which comprise mixing-"the indigo'with zinc and a solution of sodium bisulfite, the amount of bisulfite being insufficient to react with all of the zinc, and during the reduction adding sulfuric acid from time to time to the mixture to form bisulfite from the normal sulfite present.

4. In a reduction of an organic compound by the action thereon of a bisulfite in conjunction with a metal adapted to react with the bisulfite, the improvement which comprises adding-thereto, during the course of the reaction, a suitable acid capable of converting the normal sulfite present to the bisulfite.

5. In the reduction of an organic compound by the action thereon of a bisulfite in conjunction with a metal adapted to react with the bisulfite, adding to the reaction mixture, containing the bisulfite in an amount retically required to react with all of the metal present, a suitable acid capable of converting the normal sulfite present .to the-bi sulfite, the amount of acid added at any one time being merely suflicient present to the bisulfite.

6. In the reduction of an organic compound by the action-thereon of sodium bisulfite in conjunction with zinc, the improvement which comprises adding sulfuric acid to the reaction mixture in such amounts that the pres ence of bisulfite is maintained.

In the reduction pound by the action thereon of sodium hithe improvement which comprises adding thereto, during the course of the reaction, a suitable acid capable of converting the normal sulfite present to the bisulfite.

8. In the reduction of indigo by the action thereon of a bisulfite in conjunction with a metal adapted to react with the bisulfite, the improvement which comprises adding thereto, during the course of the reaction, a suitable acid capable of converting the normal sulfite present to the bisulfite.

Ina process of reducing indigo by the conjoint action of sodium bisulfite and a metal adapted to react with the sulfite, the improvement which comprises mixing the indigo with a solution of the bisulfite and with less than that theoto convert the of an organic comsufiicient to convert the normal sulfite present to the bisulfite.

11. In a reduction of indigo-by the action thereon of sodium bisulfite in conjunction with zinc, the improvement which comprises adding thereto, during the course of the reaction, a suitable acid capable of converting the normal sulfite present to the bisulfite in amounts suificient to maintain the presence of bisulfite.

In testimony whereof I afiix my signature.

DONALD e. ROGERS. 

